This invention relates to an electric bell of the type which is driven by a motor as for use in a fire bell, an alarm bell or the like, and more particularly to a gong striking mechanism which is driven by a motor to strike a gong.
In a conventional electric bell as shown in FIG. 1, a pivotting plate 2, is rotationally fixed to the shaft 1 of motor 7. A counter-weight 3 is attached to one end of the plate 2 and at the other end of the plate 2 a striking hammer 4 is arranged in a slot 5 for forward and backward movement against a gong 6 upon the rotation of a motor 7. The location of the striking hammer 4 varies each time it strikes the gong 6 so that the weight balance between the two ends of the pivotting plate 2 with respect to the rotary shaft 1 of the motor 7 fluctuates during the hammer striking motion.
Moreover, when the motor 7 starts to rotate and the striking hammer 4 strikes the gong 6, the relatively long plate 2 having the counter-weight 3 at one end and the striking hammer 4 at the other end causes the motor shaft 1 to bend due to the large torque imparted on the shaft. In addition, the plate 2 moves gradually away from the shaft 1 due to the absence of a provision for fixing the shaft 1 to the plate 2. This is especially the case when the shaft is relatively small in diameter and insusceptible for the insertion of a fixing means, such as a pin, to fix the shaft 1 and the plate 2. Therefore, the bell of the type described is disadvantageous since the rotation of the motor 7 is not uniform and tends to fluctuate. Further, the shaft 1 is subjected to bending force which causes irreparable damages thereto.
In order to overcome the above disadvantage, a bell as shown in FIG. 2 has been proposed. This bell contains a supporting plate 15 and a semi-circular gong 13 attached thereto. An electric motor 10 is mounted on the supporting plate 15. The end of the shaft 9 of the motor 10 extending from the motor is fixedly attached by a cam 8 to one end of a crank rod 11. The crank rod 11 is positioned perpendicular to the axial direction of the shaft 9. The other end of the crank rod 11 is attached to one end of a spring plate 12. The spring plate 12 is positioned perpendicular to the crank rod 11 and parallel to the axis of the shaft 9. The other end of the spring plate is fixed to the supporting plate 15. A hammer 14 is attached to the spring plate 12 between the supporting plate 15 and crank rod 11. The hammer 14 is positioned perpendicular to the spring plate 12 facing in the direction of the gong 13. When the motor 10 is energized the rotational movement of shaft 9 is converted to a reciprocal motion on the crank rod 11 by means of cam 8. The reciprocal motion of the crank rod 11 is transmitted to the spring plate 12 and hammer 14, the hammer thus striking the gong 13.
In the bell as described above, however, some problems exist such as the plurality of assembly processes required, and the cost of the bell. In addition, it is difficult to adjust to get an optimum sound volume.
Accordingly, it is an object of this invention to provide a novel gong striking mechanism in which all of the above-described drawbacks accompanying a conventional gong striking mechanism are overcome. Another object of the invention is to provide a mechanism which is reliable, and which employs simple constitutional elements to eliminate difficulties in manufacturing and in adjusting bell sound volume.
With the above and other objects in view, the invention provides a gong striking mechanism comprising a driving electric motor mounted on a frame within a gong, and conversion means rotationally connected directly or indirectly to the motor shaft for converting continuous rotational motion of the motor shaft to reciprocal gong striking motion. Preferably the conversion means comprises an eccentric cylinder fixed to the motor shaft, and a hammer made of hollow cylinder in spaced arrangement with the eccentric cylinder. The conversion means may be either a combination of a cylindrical cam and a hammer fixed to the end of a cam follower engaging with a groove formed on the cam surface, or a combination of gears and pivotting plates between which at least one hammer is rotatably mounted around an axis in a spaced arrangement between the axis and the hammer.
The novel features which are considered characteristic of the invention are set forth in the appended claims. This invention itself, however, as well as other objects and advantages thereof will be best understood by reference to the following detailed description of illustrative embodiments, when read in conjunction with the accompanying drawings.